As the use of computers and especially handheld or mobile electronic devices continues to increase at a rapid rate, the demand for peripherals and systems connected via wireless connections continues to increase. The number of wireless applications is currently increasing at a very high rate in areas such as security alarms, networking, personal computing, data communications, telephony and computer security.
Wireless communications currently may take many forms such as ultrasonic, IR and RF. In the case of RF communications, wireless transmitters, receivers and transceivers use one or more antenna elements to convert an electrical RF signal to and from an electro-magnetic wave. During transmission, the antenna serves as a radiator, generating the electromagnetic wave. During reception, the antenna serves as an absorber, receiving the electromagnetic wave.
An antenna is a transducer designed to transmit and/or receive radio waves which are a class of electromagnetic waves. Antennas function to convert RF electrical currents into electromagnetic waves and to convert electromagnetic waves into RF currents. Antennas are used in systems such as radio and television broadcasting, point-to-point radio communication, Wireless Local Area Network (WLAN), Broadband Wireless Access (BWA), radar, and space exploration.
An antenna typically comprises an arrangement of electrical conductors that generate a radiating electromagnetic field in response to an applied alternating voltage and the associated alternating electric current. When placed in an electromagnetic field, the field induces an alternating current in the antenna and a voltage is generated between its terminals.
An antenna is an electrical element having defined resonance frequencies and bandwidth. The resonant frequency of an antenna is related to the electrical length of the antenna (i.e. the physical length of the wire divided by its velocity factor). Typically, an antenna is tuned for a specific frequency and is effective for a range of frequencies usually centered around the resonant frequency. Other properties of the antenna (especially radiation pattern and impedance), however, change with frequency.
Communication and computing device manufacturers face an ongoing challenge to miniaturize electronic components. This challenge also applies to antenna design where the antenna's physical dimensions are strongly linked to the component's performance. As the physical size of communication devices shrink, manufacturers are compelled to shrink the size of the antenna systems as well.
One such area where component miniaturization is crucial is digital video broadcasting. Digital Video Broadcasting-Terrestrial (DVB-T) is the standard for the broadcast transmission of digital terrestrial television. This system transmits a compressed digital audio/video stream, using OFDM modulation with concatenated channel coding (i.e. COFDM). DVB-T is being adopted primarily for digital television broadcasting. Using OFDM, the wide-band digital signal is split into a large number of slower digital streams which are all transmitted on a set of closely spaced adjacent carrier frequencies.
Digital Video Broadcasting-Handheld (DVB-H) is a mobile TV format specification for bringing broadcast services to mobile handsets. DVB-H technology is a superset of the DVB-T system for digital terrestrial television, with additional features to meet the specific requirements of handheld, battery-powered receivers.
MediaFLO (forward link only) is a technology introduced by Qualcomm to broadcast data to portable devices such as cell phones and PDAs. Broadcast data can include multiple real-time audio and video streams, individual, non-real time video and audio “clips”, as well as IP Datacast application data such as stock market quotes, sports scores, and weather reports. The data transmission path in MediaFLO is one-way, from the tower to the device. The MediaFLO system transmits data on a frequency separate from the frequencies used by current cellular networks. In the United States, the MediaFLO system will use frequency spectrum 716-722 MHz, which was previously allocated to UHF TV Channel 55.
Additional digital video standards include, for example, the Korean T-DMB standard and the European DVB-H standard.
Ultra-High Frequency (UHF) is a frequency band used primarily for television broadcasts between approximately 474 MHz and 862 MHz. Very-High Frequency (VHF) is a lower band between approximately 200 and 300 MHz. Up until recently, most UHF television transmissions were analog (i.e. the ubiquitous high gain Yagi roof antennas or “rabbit ears” antennas) until satellite (also rabbit ears). Both transmission and reception were stationary, allowing a user to point the antenna towards the nearest transmitter and obtain a relatively good link. Analog transmissions, however, will soon be obsolete in February 2009 in the United States. The old analog transmissions are being replaced with digital broadcasting due to spectrum crowding caused by the fact that analog transmissions are not efficient in frequency.
Typically, an antenna is designed for a certain band of frequencies. The antenna is related to the wavelength of radiation the antenna is supposed to receive. A fairly efficient antenna can be constructed with λ/2. A monopole type of antenna at λ/4 is less efficient but operative. The λ/4 antennas are the most prevalent type used in handheld devices such as mobile communication devices, e.g., cell phones. Full λ antennas are not practical since they are too long at the frequencies of interest. For example, the length of a 30 MHz one λ antenna is 10 meters.
It would therefore be desirable to have an antenna system that is capable of covering the desired frequency band while having minimal physical dimensions. The miniaturized antenna preferably covers multiple frequency bands without requiring an increase in physical size.